Method for fabricating an orifice fitting for a gas pressure differential-measuring system

ABSTRACT

An orifice fitting for a gas pressure differential-measuring system is constructed of a fabricated body. In the fabrication, two lengths of flared or flanged pipe are inserted through the internal bores of respective orifice blocks and circumferentially welded on the outside. A U-member, which may be assembled of three straight pieces, is welded between the two blocks joining them and leaving a slot at the top. An orifice holder dependingly secured to a cover is provided with an orifice plate rimmed within a gasket and inserted through the slot. The cover is removably, sealingly mounted on the body. The outer face of the upstream face of the gasket is radially notched to equalize pressure in the orifice chamber.

This is a division of application Ser. No. 436,458 filed Oct. 25, 1982,now U.S. Pat. No. 4,422,339 issued Dec. 27, 1983.

BACKGROUND OF THE INVENTION

In piping systems for conducting gaseous fluid e.g. natural gas from oneplace to another, e.g. in connection with producing, gathering,collecting, processing, and/or transporting the gas, the need generallyarises for measuring gas flow characteristics. For instance, it isconventional to partially obstruct the bore of the piping at a selectedsite using an orifice plate, and to measure differential pressure usingtaps located immediately upstream and downstream of the orifice plate.

Occasionally, there is a need to change-out the orifice plate, eitherbecause mechanically or chemically effected corrosion has changed itsorifice size and shape, rendering collected differential pressure datadifficult to interpret, or system flow characteristics have changed, sothat a differently sized and/or shaped orifice is wanted.

Accordingly, there has arisen in the prior art orifice fittings, i.e.orifice plate holders which can be permanently mounted in a pipingsystem, and from which the orifice plate may be removed and replacedwith only partial disassembly of the orifice fitting itself, and with noneed to either completely dis-install the orifice fitting, nor to jackthe piping apart at the orifice fitting or partially disassemble thepiping system.

However, in most instances, the prior art orifice fittings have beenmanufactured using castings and/or forgings for the orifice fittingbodies and other major parts. That has contributed excess weight, bulkand expense to the devices, and has necessitated either that themanufacturer build ahead for inventory in order to be able to fillorders in a reasonable time, or it has meant a long delay betweenreceipt of an order and shipment of the goods. All of this is lesstolerable in the marketplace of today than it once was.

Further, in most instances, the prior art orifice fittings have beenfactory-supplied with end connections which require that the userfabricate pipe nipples to the opposite ends in the field. This can proveinconvenient or troublesome, especially where the installer damages thebody while attempting to field-attach pipe nipples to its endconnections. Further, this field work may unacceptably add to the costof making the installation due to excess labor and inspection costs.

SUMMARY OF THE INVENTION

An orifice fitting for a gas pressure differential-measuring system isconstructed of a fabricated body. In the fabrication, two lengths offlared or flanged pipe are inserted through the internal bores ofrespective orifice blocks and circumferentially welded on the outside. AU-member, which may be assembled of three straight pieces, is weldedbetween the two blocks joining them and leaving a slot at the top. Aorifice holder dependingly secured to a cover is provided with anorifice plate rimmed within a gasket and inserted through the slot. Thecover is removably, sealingly mounted on the body. The outer face of theupstream face of the gasket is radially notched to equalize pressure inthe orifice chamber.

Thus the invention provides a device for use in a gas pressuredifferential flow-measuring system, wherein the device is designed to bean integral part of the conduit in which it disposes an orifice platethrough which the gas must flow. In use differential pressure isconventionally detected on the two sides of the orifice plate, thisbeing a factor in determining total flow in the system.

The orifice fitting is designed so that the orifice plate can bechanged-out without disturbing the piping system.

In fabricating the body of the device from steel plate, an improvementover prior art devices made of cast steel is achieved, in that tightmachining tolerances can be held, manufacturing costs can be kept down,and delivery times can be made short.

The insertion of flared or flanged pipe from the inside into bores inthe orifice blocks permits the protruding stubs to be circumferentiallywelded to the outer faces of the orifice blocks to provide hub rings ofdesired length (e.g. a few inches to several feet). This method alsoallows accurate machining of the opposing sealing surfaces forengagement of the gasket assembly which houses the orifice plate.Accurate placement and machining of the the orifice tap passages also isfacilitated. Use of flared pipe also provides the advantage of avoidinginternal welds in the conduit.

By preference, the orifice plate sealing gasket assembly is slotted onone side in order to equalize the orifice chamber-to-line pressure.

The principles of the invention will be further discussed with referenceto the drawings wherein a preferred embodiment is shown. The specificsillustrated in the drawings are intended to exemplify, rather thanlimit, aspects of the invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings

FIG. 1 is an exploded perspective view of an orifice fitting constructedin accordance with principles of the present invention;

FIG. 2 is an assembled perspective view thereof;

FIG. 3 is a further-exploded perspective view of the body of the orificefitting;

FIG. 4 is a side elevation view of one of the orifice block assembliesthereof, with a portion broken away to show details;

FIG. 5 is an inner end elevation view of that orifice block assembly,with another portion broken away to show details; and

FIG. 6 is a longitudinal vertical sectional view of the assembledorifice fitting.

FIGS. 7-12 are respective similar view of a second, presently preferredembodiment of the orifice fitting.

DETAILED DESCRIPTION

The purpose of the orifice fitting device 10 is to dispose inbriefly-constricting relation at a site in a system of piping an orificeplate 12 having an orifice 14, so that pressures immediately upstreamand downstream of the orifice can be measured via pressure taps 16. Theorifice plate 12, its orifice 14, and the way in which pressure ismonitored via the taps 16 are all utterly conventional. Elements 96 areplugs for conventionally closing a set of taps 16 not in use. What isnew is that the device 10 is made in a different way, e.g. so that itmay be about as large as a thick luncheon-sandwich, instead of about aslarge as a football, for devices of comparable utility. Also by makingthe device differently, it can be made more quickly, and more accuratelyat less expense, and be easier to install and service.

As shown in the first exploded perspective view, FIG. 1, the device 10is seen to include a body 18, a cover gasket 20, and orifice holderassembly 22, bolts and lockwashers 24, 26 for removably, sealinglysecuring the orifice holder assembly on the body 18, and an orificeplate and seal assembly 28 comprising the orifice plate 12 sandwichedbetween two sealing rings 30, 32 of an orifice gasket.

The orifice holder assembly 22 includes as a cover 34 a generallyrectangular, (e.g. 5.5 inch by 3.62 inch by 0.5 inch), horizontal steelplate or bar having a pattern of four holes 36 bored verticallytherethrough in a rectangular pattern, and two laterally spaced,externally counterbored vertical holes 38 set on the transversecounterline. The assembly 22 further includes an orifice holder 40, e.g.made of the same type of steel plate or bar. Flat head socket screws 42fasten down through the holes 38 into corresponding upwardly-openingthreaded sockets in the upper end of the orifice holder 40 to unite theorifice plate to the cover. This provides a generally T-shaped member22, in which the orifice holder 40 vertically depends from the undersideof the cover 34. Holes 44 in device 10 are in alignment with holes 58 ingasket 20 and with holes 36 in cover 34, and are threaded to receivebolts 24.

The orifice holder 40 is provided with a relatively large opening 46horizontally through the thickness thereof, located so as to be centeredon the longitudinal axis of the device 10. The opening 46 is, typically,3.06 inches in diameter. As shown, the lower outer corners of theorifice holder preferably are relieved, e.g. by having 0.87 inch of the3.625 inch width trimmed off at a forty-five degree angle at each of thetwo lower corners 48.

The orifice and seal assembly 28 is sized so that its O.D. matches theI.D. of the orifice holder opening 46, and its thickness is somewhatgreater than the thickness of the orifice holder 40. The orifice andseal assembly 28 is seen to include a standard orifice plate 12sandwiched between two sealing rings 30, 32 made of usual material andcomprising an orifice gasket. Each sealing ring 30, 32 is shown having aflat inner face 50 which is circumferentially relieved adjacent theradially inner extent thereof so as to cooperatively define, when thetwo faces 50 are registered in confronting abutment, a radially inwardlyopening circumferential groove 52 in which the radially outer marginaledge of the orifice plate 12 is sealingly received.

The outer face 54 of the sealing ring 30 is provided with a radiallyextending notch or groove 56 extending from the I.D. to the O.D. thereoffor pressure relief purposes.

The cover gasket 20 typically is a rectangular sheet of asbestos,neoprene, or similar gasket material provided with a pattern of fourholes 58 matching that of the cover, and a laterally elongated,generally rectangular central slot 60 shaped and sized to receive theorifice holder 40.

The body 18, as fabricated, is seen to comprise a generallyrectangular-prismatic member 62 (typically 3.62 inches thick by 5.50inches wide and high), from both ends of which respective pipe stubs 64project for any selected distance from a few inches to several feet(typically 4.5 inches to nearly six feet).

The top of the body 18 is seen to be constituted by a flat, horizontalsurface 66 which includes a pattern of four upwardly-opening threadedsockets matching the patterns of the respective holes in cover and covergasket. Further, the body is centrally provided with an upwardly openingslot 68 through the surface 66. The slot has the same laterallyelongated, generally rectangular orientation and shape as the slot 60through the cover gasket 20, but it is somewhat wider and broader thanthe comparable horizontal dimensions of the orifice holder 40. (Withreference to FIG. 6, the slot 60 may also be seen to be somewhat deeperthan the as-installed orifice holder is tall.)

Accordingly, the apparatus shown in FIG. 1 may be assembled to providethe device as shown in FIG. 2, by: inserting the orifice holder 40downwards through the slot 60 in the cover gasket 20; sandwiching theorifice plate 12 between the sealing rings 30, 32 to constitute theorifice plate and seal assembly 28; inserting that assembly in the largeopening 46 of the orifice holder 40 and centering it there so that itprotrudes about as much past each face of the orifice holder; andinserting the depending bladelike portion of the resulting assembly intothe slot 68 down to the hilt, i.e. until the cover gasket 20 becomessandwiched between the flat underside of the cover 34 and the flat topsurface 66 of the body 18. Then the bolts and lock washers 24, 26 areinstalled as shown. Changing out the orifice plate 12 merely calls for adouble reversal of the steps just described.

The body 18, while being a unitary member by time it is shown in FIG. 1,is not an integral casting. Rather, it is fabricated of a small numberof parts, as will be understood by referring to FIGS. 3, 4, 5 and 6. Inparticular, the body 18 is constituted by two identical orifice blockassemblies 70 sandwiched flatwise against opposite faces of an upright,U-shaped member 72 and externally perimetrically welded at 74 in theangular direction over the outer periphery of the legs 76 and bridge 78of the U-shaped member. Typically, the U-shaped member is 0.62 inchesthick, and its outer periphery is initially indented by one quarter ofan inch top, sides and bottom, relative to the peripheries of the blockassemblies 70. In fabricating the orifice block assemblies 70 to theU-shaped member, the indentation or outer perimetrical groove is filledwith weld metal to slight excess causing a fillet 80. This is leftas-is, except for one top, where the top surface 66 is machined flatafter the welding step has been completed. The gap between the legs ofthe U-shaped member constitutes the lateral extent of the slot 68.

Further, each orifice block assembly 70 is not formed as an integralmember, but rather as fabricated of a small number of parts.Particularly, each orifice block assembly includes an orifice block 82and a flared pipe 84.

Each orifice block 82 typically is a generally rectangular prismaticmember typically 1.5 inches thick and centrally provided through itsthickness with a cylindrical bore 86. At the site of the intersection ofthe bore 86 with the flat inner face 88 of the block 82, the bore 86 iscounterbored to provide a circumferential recess 90.

The pipe 84 is substantially a right cylindrical tube, but is flaredadjacent and leading to one end to provide a radially out-turnedcircumferential flange as at 92.

The O.D. of the pipe 84 (except for the flange 92) nominally matches theI.D. of the bore 86, and the depth of the recess 90 matches the axialthickness of the flange 92. Accordingly, the pipe 84 is assembled to theblock 82 by inserting the outer end of the pipe into the inner end ofthe bore 86 and thrusting the pipe 84 axially outwards until the flange92 bottoms in the counterbored recess 90. At this time the axially innerend surface 94 of the pipe 84 is flush with the flat inner surface 88 ofthe block and an axially outer end portion of the pipe 84 protrudes outof the outer end of the bore 86 to provide a pipe stub 64. At theintersection of the pipe stub 64 with the block 82 a circumferentialweld 96 is made to unite the pipe and block into one member. Ifnecessary, the face 88 and/or the face 94 may be machined at this stageto improve the flatness of the composite planar surface.

It should be noticed that, in addition to being provided with arespective two of the sockets 44, and the counterbored bore 86, eachorifice block assembly is provided with at least one pressure tap 16,which as shown enters the respective block 82 horizontally intermediateits thickness and proceeds as a passageway parallel to the end faces ofthe block radially inwardly to and through the wall of the flared pipe84. The outer portion of the tap 16 is shown being internally threaded.In the preferred embodiment, each orifice block assembly is shownprovided with two diametrically opposed such taps 16, so that for anyparticular installation, the least accessible one may be plugged as at96, and the most accessable one conventionally used for pressuremonitoring by being connected in a conventional differential pressuremeasuring system (not shown).

The completed orifice block assemblies 70 are united with a U-shapedspacer member, and the orifice holder installed to constitute theorifice fitting 10, all, as described hereinabove. When the orificeholder is installed, an especially good seal is formed between thegasket rings 30, 32 and the respective composite flat surfaces 88/94,except for where the groove 54 is provided to equalize pressure on theslot cavity 60 on the O.D. of the gasket 30/32.

A presently preferred embodiment of the invention is illustrated at 110in FIGS. 7-12. Most parts are comparable to those of the embodimentshown in FIGS. 1-6, and so are given like numerals, raised by a constant100. Accordingly the following description is limited to pointing outthe notable differences.

In the preferred embodiment 110, the bores 186 are not counterbored atthe inner face 188. Accordingly, as the flared pipe 184 is inserted intothe bore 186 through the inner face 188, insertion proceeds until theflange 192 engages the inner face 188 perimetrically of the bore 186. Aseal, e.g. by circumferential welding is provided at 200.

Also in the preferred embodiment 110, the U-shaped member 172 isprovided as an assemblage of three straight parts, two legs 176 and abridge 178.

By preference, as the U-shaped member 178 is unitized by being welded inplace between the blocks 182, the weld material need not bridge entirelyover the outer surface of the U-shaped member 172. Rather, the weldmaterial may appear in the finished article as two individual jointbridging welds 174 with some of the central region of the outer surfaceof the U-shaped member 172 visible between them.

Further, the gasket means 30, 32 rather than being formed as two pieceswhich are assembled about the orifice plate 112, may be formed as anintegral member 130/132 which rims the orifice plate.

Lastly, the cover 134 of the orifice plate assembly preferably isprovided with a loop-shaped handle 202, welded on at the locations ofthe screws 142 (not seen).

It should now be apparent that the orifice fitting for a gas pressuredifferential-measuring system as described hereinabove, possesses eachof the attributes set forth in the specification under the heading"Summary of the Invention" hereinbefore. Because it can be modified tosome extent without departing from the principles thereof as they havebeen outlined and explained in this specification, the present inventionshould be understood as encompassing all such modifications as arewithin the spirit and scope of the following claims.

What is claimed is:
 1. A method for constructing an orifice fitting fora gas pressure differential-measuring system, comprising:(a) providingtwo block members each with an inner face and a throughbore extendingthrough that face; (b) providing two lengths of pipe, each flared at theinner end thereof to define a radially outwardly projectingcircumferential flange; (c) inserting each pipe into a respectivethroughbore through the inner face of the respective block member, withan outer end portion of that pipe protruding from the opposite end ofthe respective throughbore to provide a pipe stub extending from therespective block; (d) circumferentially welding each pipe stub to therespective block where that pipe stub emerges from the respectivethroughbore, thus providing two orifice block assemblies; (e) providinga U-shaped spacer having two legs and a bridge, presenting the twoorifice block assemblies, inner faces inwards, in sandwiching relationto the U-shaped spacer and welding about the external periphery of theU-shaped spacer, between the U-shaped spacer and both said blocks toform a unitary body having a laterally opening slot through one side,between the legs of the U-shaped spacer and in communication with theinner ends of both of said pipes; (f) machining said side of said bodyto provide for the mounting and sealing of an orifice holder assemblythereto; and (g) forming a pressure tap through each said orifice blockassembly and the respective pipe stub wall adjacent said slot.
 2. Themethod of claim 1, further comprising:(h) providing an orifice holderassembly having a generally horizontal cover with a depending orificeholder having an opening provided through the thickness thereof; (i)inserting in that opening an orifice plate rimmed with a gasket; (j)sandwiching a perimetrically extending cover gasket between said coverand said side of said body, inserting the depending orifice holdercontaining said orifice plate and gasket into said slot, and sealinglysecuring the cover of the orifice holder assembly to said body upon saidside of said body.
 3. The method of claim 2, wherein:in conducting step(a) the two block members are each provided with a counterbore at theintersection of the respective throughbore with the respective innerface; and in conducting step (c), the flared inner end of each pipe ismade flush with the respective block inner face by seating therespective flange in the respective counterbore.